Electrodeposited coatings



July 26, 1955 w p, KARASH 2,714,088

ELECTRODEPOSITED COATINGS Filed Jan. 8, 1952 I3 CHROMIUM-.Zeaazaszzaeaaezazzezze. NICKEL I2 MONY LEAD WALTER P. KARASH INVENTOR.

2,17%,088 Patented July 26, 1955 ELECTRODEPOSITED COATINGS Walter P.Karash, Cleveland, Ohio, assignor to The Harshaw Chemical Company,Cleveland, Ohio, a corporation of Ohio Application January 8, 1952,Serial No. 265,450

15 Claims. (Cl. 204-36) This invention relates to the production ofprotective inch or more, or chromium over nickel applied over a thincoating of copper. These nickel coatings, when applied to a suficientthickness and buffed, or when applied from a solution containing abrightening addition agent, are quite satisfactory for chromium plating.

Nickel, however, is expensive and sometimes difficult to 7 obtain. Aneed therefore exists for a protective and decorative coating havingsubstantially the protective and decorative effect of nickel but whichcan be produced at a lower cost and from materials which are lessexpensive and less difiicult to obtain.

Various metals havebeen considered as replacements for nickel, butdifficulties have always been encountered. Among the other metals whichhave been considered, lead is attractive from the standpoint of cost,but is too soft for most uses, and is difiicult to buff to a brightfinish. Antimony also has been seriously considered, since it is harderthan lead, affords good protection against corrosion, and is readilybuffed. Like nickel, antimony will tarnish if exposed, and musttherefore be protected. It was an obvious procedure to try protecting anantimony deposit by applying a chromium deposit thereover in accordancewith the practice in nickel plating, chromium over nickel over steelbeing a very common type of coating for automobile trim, plumbingfixtures and many other uses. When, however, it was attempted toelectro- I deposit chromium on a bright (image reflecting) antimonysurface it was found that the resulting chromium deposit was not bright.

I have now discovered that a bright, adherent, chromium deposit can beapplied over a bright antimony surface by interposing between suchantimony surface and the chromium a very thin nickel (or equivalent)deposit. Such nickel deposit may be exceedingly thin, for example asthin as 0.000002 of an inch. The nickel deposit may be produced in anyof various nickel plating solutions such as the Watts bath whichordinarily contains nickel sulfate, nickel chloride and boric acid butno brightening addition agent and which ordinarily produces a graydeposit. Deposits from the gray nickel solution on a bright antimonysurface are bright enough for my purposes up to a thickness of 0.00003of an inch. The deposit may also be produced in a solution which doescontain one or more brightening addition agents, but these are notdesirable unless the thickness of the nickel (or equivalent) exceedsabout 0.00003 of an inch. If the nickel (or equivalent) is depositedfrom a so-called bright plating solution or is lightly buffed to removeany slight grayness the thickness may be as much as 0.0001 of an inch. Aheavier deposit of nickel, for example such as normally used forautomobile decoration, that is, a deposit in the order of 0.001 of aninch in thickness, is not satisfactory. Such deposits exhibit pooradherence, even tend to flake off after the chromium deposit is applied.If produced in a so-called bright nickel solution, which always resultsin harder and more brittle deposits, the adherence diliiculties, thetendency to flake oif after chromium plating, would be increased for athick layer such as ordinarily used in nickel plating, althoughremaining imperceptible in the case of very thin layers. Accordingly Iprefer to use gray nickel in the thickness range from 0.000002 to0.00003 of an inch.

Ordinarily, the bright antimony surface will have been produced bybufling and then thoroughly cleaningan electrodeposit of antimony, theproduction of which as an adherent coating on steel is known to the art.For example, Bloom (U. S. Patent No. 2,389,131) describes a method ofetching the steel and plating on the resulting surface from an antimonytrifiuoride bath containing a monovalent fluoride and operating at a pHsomewhat below 6.0. By the use of suitable addition agents bright (asplated) deposits of antimony can be obtained. The older literaturedescribes the use of the antimony trifiuoride bath with sodium orpotassium fluoride, also antimony trifluoride with sulfuric acid,sometimes SbF3 with free HF. (See Metal Cleaning and Finishing, vol 7,page 339.) Tartrate, citrate, and oxalate antimony plating solutions arealso described in the literature. The particular plating solutions bymeans of which the antimony and other deposits are produced do not, perse, form any part of the present invention, the foregoing being citedmerely to indicate that antimony plating solutions and processes areavailable and form a part of the knowledge of the operator skilled inthe art. Lead, nickel, chromium, etc. plating also are well establishedarts.

It the primary object is to form a protective and decorative coating onsteel or any of numerous other metals and alloys a very excellentprocedure is to apply first an electrodeposit of lead, tin, silver oralloys thereof which are easily applied to steel, zinc base diecastings, copper, copper plated die casting, brass, lead base and pewtercastings, etc. Adherent antimony deposits are easily applied to unbuifedlead, tin or silver, or lead, tin or silver alloy electrodeposits in theform of adherent coatings which can be readily buffed to a high lustre.On the buffed antimony, there may be then applied a very thin coating ofnickel or cobalt or, less desirably, zinc, copper, white brass or iron.Over the resulting thin deposit there is applied an electrodepositedcoating of chromium, suitably of a thickness of the order of 0.00001 ofan inch, which will not be dull, as in the case where it is plateddirectly on polished antimony, and which will not cause a separation ofthe thin nickel (or the like) deposit from the antimony, as whenrelatively heavy deposits of nickel are applied on the antimony andfollowed by chromium.

So far as I am aware, no one has heretofore realized that chromium couldbe applied as a brilliant, strongly adherent coating over brightantimony by interposing a thin coating of nickel, cobalt or the like. Itis perhaps surprising that the chromium deposit would not turn outbright when applied over highly polished antimony, but that has beenfound to be what happens; and while it would be expected from nickelplating practice that a bright chromium deposit could be applied on abright nickel surface, it is surprising that an ultrathin layer ofnickel would result in overcoming the tendency of chromium to plate dullover polished antimony and at the same time retain excellent adhesion inthe case of thin layers only of nickel, cobalt or the like.

In the accompanying drawing, the figure is a schematic with usualpolishing compounds.

representation of a multiple-layer deposit according to the invention,wherein the thicknesses are greatly exaggerated, and wherein thebufifing step is indicated by a schematic representation of abuffing-wheel applied on the surface which is buffed.

In the drawing, the numeral indicates the base metal to be coated,which, as indicated, may be steel or zinc base die casting metal,copper, brass, pewter, etc. Electrodeposited on the base metal is theoptional layer 11 of lead which, it is to be understood, may be omittedif suit able care is taken to apply a strongly adherent coating ofantimony on the base metal, or which may be replaced by tin or silver.The antimony deposit 12 must be strongly adherent, and should be of athickness great enough that, upon being buffed, there is no danger ofcutting through and exposing the underlying layer. The antimony depositnormally may be of a thickness of about 0.0003 of an inch, andpreferably is of a thickness of the order of 0.0005 to 0.002 of an inch.A thickness from 0.00075 to 0.0015 of an inch should prove adequate forany reasonable amount of bufling. The antimony deposit is buffed to abright finish, as indicated by the schematic indication of abufiing-wheel 13 in contact with its surface, and thereafter there isapplied the ultrathin coating 14 of nickel or cobalt (less desirablycopper, zinc, iron or white' brass). This coating may be of a thicknessfrom 0.000002 to 0.0001 of an inch, but preferably is from 0.000002 to0.00003 ofan inch in thickness. The chromium deposit 15 is applied overthe ultrathin coating 14 of nickel, cobalt V or the like.

It should be emphasized that even though Bloom and others, especiallyMathers, Trans. Am. Electrochem. Soc. 31, 289 (1917), found solutions tothe problem of forming satisfactory electrodeposits of antimony, and thefurther fact that antimony is cheaper than nickel, the use of antimonyfor protective coating of metals has not become widespread. Whileantimony deposits are brittle, they do on buffing form good, bright,corrosion resistant coatings which, however, soon tarnish in air to anextent that their brightness is not restored by polishing Attempts toapply chromium over buffed antimony were highly successful as toadherence, but the brightness was lost. For example, 0.001" of antimonywas applied on steel from an aqueous solution containing 250 grams perliter of SbFs and 200 grams perliter NHiF at a pH of 4.5, temperature130 F. and cathode current density of amperes per square foot. Theresulting deposit was bufied to a high lustre and chromium was appliedto a thickness of 0.00001" from an aqueous solution containing 250 gramsper liter of CrOa and 2.5 grams per liter of sulfate ion, operated at atemperature of 113 F. and a cathode current density of 150 amperes persquare foot (initially about 280 amperes per square foot for starting).The resulting deposit was firmly adherent but cloudy. The experiment wasre- 7:

peated with the exception that after buffing the antimony deposit therewere applied to each of four buffed antimony electrodepositsrespectively nickel deposits of thicknesses approximately 0.000002,0.00002, 0.0001 and 0.001 from, in each case, an aqueous solutioncontaining 240 g./l. of NiSO4.6H2O, 40 g./l. of NiCl2.6I-I2O and 40g./l. of H3BO3. Chromium was then applied as before. In each of thefirst two instances the deposit was firmly adherent and fully bright. Inthe case of the deposit 0.0001 thick, it was firmly adherent afterchromium plating but not fully bright. Adding brightening additionagents to the solution resulted in a fully bright, firmly adherentdeposit after chromium plating at a thickness of 0.0001" of'nickel. (Thebrightening addition agent may be any commercially obtainablebrightener, e. g., 2 g./l. naphthalene disulfonic acid and 0.002 g./l.fuchsin.) In the case of the deposit 0.001" thick, the deposit wasbright but not firmly adherent, tending to flake off easily. Cobalt insimilar thicknesses was found to be the full equivalent of nickel exceptfor its higher cost. Iron,

copper, zinc and white brass in similar thicknesses gave fairlycomparable results but proved more difficult to control.

Plating solutions suitable for the electrodeposition of antimony, lead,nickel, cobalt, zinc, iron, copper and white brass are as follows:

(1) SbF g./l 250 NHiF g./l 200 pH 4.5 Temperature F 130 (2)SbF3(NH4)2SO4 g./l 400 pH 4.0 Temperature F 130 (3) Pb(BF4)2 oz./gal33.5 HBF4 oz./gal 10.7 H3BO3 oz./gal 3.0

Glue oZ./gal .03-.06

1 pH 4.0 Temperature F 120 (4) NiSO4.6H2O g./l 250 NiClz.6H2O g./l H3303g./l 35 pH 4.0 Temperature F 120 (5) NiSO4.6HzO g./l 100 NiCl2.6H2O g./ll5 H3BO3 g./l 30 0 pH 3 0 Temperature Room The antimony surface must bewell cleaned before nickel is applied.

35 (6) C0Cl2.6H2O g./l 100 NH4F.HF g./l 20 pH 3.0 Temperature F 130 40(7) Zn(CN)2 g/l NaCN g./l 42 NaOH g./l 79 NazS g./l 0.75 Temperature F80 (8) FeSO4.7I-Iz0 g./l 200 NaBF4 g./l 40 pH 3.0 Temperature F (9) CuCNg./l 120 Free cyanide g./l 3.75

Water Remainder pH 10.5 Temperature F '3 (l0) Zn(CN)2 g./l 60 Cu(CN)g./l 14 NaOH g./l 60 NaCN g./l 52 Na2SO3 g./l 0.48

= Temperature F 90 Having thus described my invention, what I claim is:

l. A process of producing a bright, electrodeposited coating whereinchromium is applied subsequent to antimony comprising electrodepositingon a bright antimony metal surface a film of a metal of the classconsisting of nickel, cobalt. zinc, iron, white brass and copper of athickness from 0.000002 to 0.0001 of an inch and electrodepositing alayer of chromium over said film, said bright antimony metal surfacebeing the surface of an elec tin-deposit of antimony on and firmlyadherent to a metallic base.

2. A process comprising electrodepositing on a bright tony metal surfacea film of a metal of the class cong of nickel, cobalt, zinc, iron, whitebrass and copper of a thickness from 0.000002 to 0.0001 of an inch andelectrodepositing a layer of chromium over said film, said brightantimony metal surface being the surface of an electrodeposit ofantimony on and firmly adherent to a metallic base of the classconsisting of lead, tin, and silver.

3. A process comprising electrodepositing on a bright antimony metalsurface a film of a metal of the class consisting of nickel, cobalt,zinc, iron, white brass and copper of a thickness from 0000002 to 0.0001of an inch and electrodepositing a layer of chromium over said film,said bright antimony metal surface being the surface of anelectrodeposit of antimony on and firmly adherent to a metallic base ofthe class consisting of lead, tin, and silver applied on steel.

4. A process of producing a bright, electrodeposited coating whereinchromium is applied subsequent to antimony comprising electrodepositingon a bright antimony metal surface a film of nickel of a thickness from0.000002 to 0.0001 of an inch and electrodepositing a layer of chromiumover said film, said bright antimony metal surface being the surface ofan electrodeposit of antimony on and firmly adherent to a metallic base.

5. A process of producing a bright, electrodeposited coating whereinchromium is applied subsequent to antimony comprising electrodepositingon a bright antimony metal surface a film of cobalt of a thickness from0.000002 to 0.0001 of an inch and electrodepositing a layer of chromiumover said film, said bright antimony metal surface being the surface ofan electrodeposit of antimony on and firmly adherent to a metallic base.

6. A process comprising electrodepositing on a metal base a layer ofantimony metal having a bright surface, electrodepositing on said brightantimony metal surface a film of a metal of the class consisting ofnickel, cobalt, zinc, iron, white brass and copper of a thickness from0.000002 to 0.00003 of an inch and electrodepositing a layer of chromiumover said film, said bright antimony metal surface being the surface ofan electrodeposit of antimony on and firmly adherent to a metallic base.

7. A process comprising electrodepositing on a metal base a layer ofantimony metal having a bright surface, electrodepositing on said brightantimony metal surface a film of nickel of a thickness from 0.000002 to0.00003 of an inch and electrodepositing a layer of chromium over saidfilm.

8. A process comprising electrodepositing on a metal base a layer ofantimony metal having a bright surface, electrodepositing on said brightantimony metal surface a film of cobalt of a thickness from 0.000002 to0.00003 of an inch and electrodepositing a layer of chromium over saidfilm.

9. A process comprising the steps of electrodepositing on a metallicbase a layer of antimony metal, bufiing said layer of antimony metal toproduce a bright surface thereon, electrodepositing on the resultingbuffed surface a film of nickel of a thickness from 0.000002 to 0.00003of an inch, and then electrodepositing a layer of chromium over saidfilm.

10. A process according to claim 9 wherein said layer of antimony iselectrodeposited on an electrodeposited layer of a metal of the classconsisting of lead, tin and silver on a base metal.

11. A process comprising the steps of electrodepositing on a metallicbase a layer of antimony metal, bufiing said layer of antimony metal toproduce a bright surface thereon, electrodepositing on the resultingbuffed surface a film of nickel of a thickness from 0.000002 to 0.0001of an inch, and then electrodepositing a layer of chromium over saidfilm.

12. A process according to claim 11 wherein said layer of antimony iselectrodeposited on an electrodeposited layer of a metal of the classconsisting of lead, tin and silver on a base metal.

13. A process comprising the steps of electrodepositing on a metallicbase a layer of antimony metal, buffing said layer of antimony metal toproduce a bright surface thereon, electrodepositing on the resultingbulfed surface a film of cobalt of a thickness from 0.000002 to 0.00003of an inch, and then electrodepositing a layer of chromium over saidfilm.

14. A process according to claim 13 wherein said layer of antimony iselectrodeposited on an electrodeposited layer of a metal of the classconsisting of lead, tin and silver on a base metal.

15. A process comprising the steps of electrodepositing on a metallicbase a layer of antimony metal, bufiing said layer of antimony metal toproduce a bright surface thereon, electrodepositing on the resultingbufied surface a film of cobalt of a thickness from 0.000002 to 0.0001of an inch, and then electrodepositing a layer of chromium over saidfilm.

References Cited in the file of this patent UNITED STATES PATENTS1,061,674 Hoyt May 13, 1913 1,087,561 Tebbetts Feb. 17, 1914 1,738,748Wirshing et al. Dec. 10, 1929 1,792,082 Fink et al Feb. 10, 19311,836,598 Humphries Dec. 15, 1931 2,093,428 Ford et al Sept. 21, 19372,637,686 McKay May 5, 1953 2,658,266 Du Rose et al Nov. 10, 1953

1. A PROCESS OF PRODUCING A BRIGHT, ELECTRODEPOSITED COATING WHEREINCHROMIUM IS APPLIED SUBSEQUENT TO ANTIMONY COMPRISING ELECTRODEPOSITINGON A BRIGHT ANTIMONY METAL SURFACE A FILM OF A METAL OF THE CLASSCONSISTING OF NICKEL, COBALT, ZINC, IRON, WHITE BRASS AND COPPER OF ATHICKNESS FROM 0.000002 TO 0.0001 OF AN INCH AND ELECTRODEPOSITING ALAYER OF CHROMIUM OVER SAID FILM, SAID BRIGHT ANTIMONY METAL SURFACEBEING THE SURFACE OF AN ELECTRODEPOSIT OF ANTIMONY ON AND FIRMLYADHERENT TO A METALLIC BASE.